Unlike a lot of the other whining, non-issue complaint threads out there, this is an actual and definite problem in the game and I just thought I'd post in this thread too in hopes of a timely response from the devs.
I have played WoW for a number of years (spaced apart) in vanilla, TBC, and WotLK with some raiding experience but I definitely am not a hardcore player. When it comes to PVP, I'd say that I'm more on the side of awful than casual with my incredibly slow reaction times. That being said, the ability delay is undeniably there and truly mucks up the combat experience.
For a long time, I didn't even know exactly what was wrong and had no way to label what I noticed was occurring. I read somewhere that Riposte is a key ability for Jedi Guardian tanks and that I should use it every chance I get. But when I tried putting this advice into use, I kept noticing that despite pressing the keybind for the ability, nothing happened. At first, I placed the blame on myself and assumed that I never had the proper amount of Focus in the first place to use it. But as I continued to use it while purposely taking extra steps to ensure that I had extra Focus, there would still be so many times where I would need to button mash the key before the actual ability went off.
While Riposte is the ability that I noticed this delay the most, I can say for certain that other abilities (not exactly sure which) still feel sluggish. As a Jedi Guardian tank I know that my DPS is going to be lacking, but it's to the point where I feel like my companion is crucial to clearing these groups of mobs. That issue with targeting certainly does not help with that sluggish combat feeling... but I guess that's an issue for another thread.
While PVPers will certainly feel this delay keenly, I can see it as a PVE problem too. Since I haven't gotten that far in the game I can't say this from experience, but I can see this being a problem for my threat generation. Unless abilities go off when they're supposed to, it's not hard to imagine how that will cause a wipe when I can't keep aggro. While I am most likely a bad tank (this is my first time playing one), I'd rather not get extra hate for a wipe that isn't entirely my fault...
Is this a game breaking issue? I'm not sure. I certainly will keep on playing for the moment since I am enjoying many aspects of the game (while acknowledging it's far from perfect). I certainly hope that this issue as well as other valid concerns about the game are addressed ASAP. I guess I'm on the forgiving and optimistic side but I'm not so sure how long my PVP loving friends will endure the problems... and if they leave it makes it that much harder and less likely for me to stay...